gt2876 EGT's vs gt2860rs EGT's

[Bush65]

so does anyone know would a the smaller trim spool up faster or wat the effect would be between the the smaller and larger trim?

Simplistically:
Compressor trim is ratio of inducer (inlet) area to exducer (outlet) area as a percentage,
i.e. trim = (inducer^2 / exducer^2) x 100 (use inducer and exducer diameters)

Now the inducer area has greatest affect on air flow - bigger diameter/area flows more air, but more flow increases the load on the turbine, so will be slower to spool up.

From the trim formula, you can see that for same exducer diameter, the inducer is larger if the trim is larger.

Boost pressure is related to the tip speed squared - crudely speaking, a centrifugal compressor develops pressure by throwing the air at speed (stick your hand out the car window as the speed increases the pressure increases). Compressoe tip speed is a function of exducer diameter and rpm.

Trim also give a good idea of compressor efficiency (how much heat is added to the air while increasing the boost pressure. Small trim will give better efficiency for same boost pressure - because the small trim results from a smaller inducer, the air flowing from the inducer to the exducer is in contact with the blade for a greater distance (so the blade is more efficient at getting the air up to the speed of its tip when it exits).

Hope that explanation helps.

[GU-ish]

thanks that helped heaps, think ill go for the smaller 48 inducer with the .64 hot side.
peoples opinions?

[CustomTurbos]

How much boost you make and how early it is made in the rev range is tied very closely to the amount of fuel you are squirting in. More fuel = higher EGT = more exhaust energy and more boost.

Having said that, it doesnt mean trim isnt important, you may end up with alot of smoke, compressor surge or likely both trying to build boost earlier than the overall turbo spec to motor spec allows.

The 151rwkw was ~ 3000rpm, but held most of the power nicely through the revs. As a result, while the turbo was maxed out at 3000rpm ~ 23psi, the turbo wasnt put into overspeed because the pump was tuned to drop the cc's being pumped with rpm above this point, but not like a mountain cliff. It meant a nice over rev was available. Over rev meaning usable power above the max power rpm that may be called upon if you need to hold a gear long for example.

In this vehicles case, 18psi was available with smoke from 1600rpm. If you try and tune the smoke away to more acceptable levels, boost was strong probably some 500rpm later.

Regarding turbo trim; you cant compare the trim of one compressor wheel to another if their diameters are different. The formula for trim is Trim = (inducer dia/exducer dia)^2. As a generalisation, a higher trim compressor will have a higher choke flow and will have a worse surge line and will be higher in efficiency. the 0.62 trim 60mm comp wheel is a very efficient beast. My cousins GT2860RSD was damaged due to surge - axial play - (but actually died due to mud....) because he wanted the amazing wide torque band in his races. All you need is a programmable boost controller (max boost vs rpm) to fix this, but he didnt bother as he had other plans.

A larger diameter comp wheel on any given turbine will require more torque to drive it, thus there is less chance that a GT2871 48 trim (49.2mm inducer) will hit surge compared to a GT2860RS 62 trim 47.2mm inducer) even though the 71mm has a higher flow potential. Also because the efficiency of the 71mm 48 trim comp wheel is lower near the surge line than the 62 trim 60mm wheel, this serves to reduce the tendency for surge.

But, surge aside (because using a boost controller and properly profiled aneroid it can be avoided) the GT2860RS will likely be a less smokey turbo due to higher efficiency in its operating range since it needs less backpressure to make the same boost or alternatively can make more boost at a given fueling rate = leaner

I for one think that both turbos will probably work fine. I am not keen on having an inducer bigger than the turbine exducer on a diesel since more reliance is on the wastegate = less eficiency at the top of the revs = high egts, thus in my opinion the 47.2mm inducer is near on a perfect match to the 48 odd mm turbine exducer. Typically ~ 7% additional mass flow is out the exhaust, so if you need turbo efficiency - and diesels do due to low egts compared with a gasser - you should probably select a turbo first by turbine, then select inducer size, then select compressor trim (in this case, wheel diameter) based on turbine trim and AR ratio so that you keep efficiency as high as possible without hitting surge.

You could say another way, not forgetting comments on the turbine, design the comp wheel around max choke flow, that will give you the widest performance window, then keep trim as high as possible without surge, that will keep yours smoke low and faster spool.

Thats my 2c anyway - more than one way to skin a cat

[CustomTurbos]

so does anyone know would a the smaller trim spool up faster or wat the effect would be between the the smaller and larger trim?

Simplistically:
Compressor trim is ratio of inducer (inlet) area to exducer (outlet) area as a percentage,
i.e. trim = (inducer^2 / exducer^2) x 100 (use inducer and exducer diameters)

Now the inducer area has greatest affect on air flow - bigger diameter/area flows more air, but more flow increases the load on the turbine, so will be slower to spool up.

From the trim formula, you can see that for same exducer diameter, the inducer is larger if the trim is larger.

Boost pressure is related to the tip speed squared - crudely speaking, a centrifugal compressor develops pressure by throwing the air at speed (stick your hand out the car window as the speed increases the pressure increases). Compressoe tip speed is a function of exducer diameter and rpm.

Trim also give a good idea of compressor efficiency (how much heat is added to the air while increasing the boost pressure. Small trim will give better efficiency for same boost pressure - because the small trim results from a smaller inducer, the air flowing from the inducer to the exducer is in contact with the blade for a greater distance (so the blade is more efficient at getting the air up to the speed of its tip when it exits).

Hope that explanation helps.

I just realised that I made a point that contradicted one of yours. Indeed I hadnt read your post when I typed out mine.

The point is regarding compressor efficiency. I have seen a pattern that higher trim compressor wheels of the same generation of design generally increase in efficiency and width of efficient area on the map as the trim is increased. I have understood that this is because the compressor heads towards a combination of centrifugal and axial flow as the inducer increases relative to the exducer. In addition, lowering the trim reduces the length of the contact area and traversing distance which serves to reduces boundary frictional heating of the air.

[CustomTurbos]

thanks that helped heaps, think ill go for the smaller 48 inducer with the .64 hot side.
peoples opinions?

If your going smaller, the 62 trim 60mm comp wheel is smaller - 47.2mm inducer

The 0.64 A/R GT28 hot side is not even worth worrying about - it is well documented that it is the best off the shelf ratio available. So really the best option is to look at the comp wheel. 151rwkw is available from the smaller wheel also with not much smoke = nice and clean. So if your pump doesnt flow more than 115cc, there no point going for a larger compressor wheel inducer.

IF you flow 109cc @ 3300rpm or less, I would seriously consider the turbo from a 1HDFTE - 46mm inducer, 50 trim, same size turbine but I *think* the exhaust housing is close to 0.55. It is a solidly built turbo and isnt ball bearing - personally I think that is a good thing. You can also get adaptor flanges to convert t3 to the Toyota flange spec. I calculate 142rwkw @ 22psi @ 3300rpm with 109cc fuel may be possible on a TD42 with this turbo with top spec intercooler and exhaust. Best of all, peak torque from ~ 1400rpm! You would need to find one of these turbos though, thats the hard part.

[GU-ish]

well i just ordered the 2871 r .64 hot side, A/R60 and trim 48
dunno if anyone has used this before but i thought id give it ago after reading lost of info from alot if differnt places

thanks for ya help

[CustomTurbos]

well i just ordered the 2871 r .64 hot side, A/R60 and trim 48
dunno if anyone has used this before but i thought id give it ago after reading lost of info from alot if differnt places

thanks for ya help

Well, I am sure you will not be dissapointed - alot have used this exact turbo. My points were really more about that last bit of optimisation.

What cc's does your pump flow? Would be great to hear your results.

All the best with the project

[KiwiBacon]

so does anyone know would a the smaller trim spool up faster or wat the effect would be between the the smaller and larger trim?

Yes it will spin up a little sooner. But of bigger concern is the different trim wheels have quite different compressor maps. You need to match what you want from the engine and turbo to what the turbo can do.

[GU-ish]

my pump is a standard GU pump. going to leave it stardard till i got the cash to do it up.
yeh once its on ill be happy to post up how it goes, after all its so hard to find info so im happy to share.

[CustomTurbos]

my pump is a standard GU pump. going to leave it stardard till i got the cash to do it up.
yeh once its on ill be happy to post up how it goes, after all its so hard to find info so im happy to share.

Great to hear how it goes. If the engine is a factory TD42T GU engine, the pumps apparantly max out at ~ 90cc and you should get ~ 520-540nm @ crank, ~ 120-130rwkw providing you have an excellent intercooler and exhaust and ~ 18psi. That is the case with the late partly electronic pump (timing electronic, fueling is still mech though)

[GU-ish]

well its a 2000 gu ute so yeah. Has a small top mount which i will soon also be changin. 3 inch exhurst no muffler and will be 3inch dump. Lookin at doin a custom air box to suit pod filter

[twodiffs]

well i just ordered the 2871 r .64 hot side, A/R60 and trim 48
dunno if anyone has used this before but i thought id give it ago after reading lost of info from alot if differnt places

thanks for ya help

Got any updates, news, pics for us yet GUish?? - no pressure mate

[GU-ish]

started on it.
here is the link to my thread in the members sections... ill keep it up dated
http://www.outerlimits4x4.com/viewtopic ... 1#p1963341" onclick="window.open(this.href);return false;

cheers
chriso

[UGOTNUFN]

my pump is a standard GU pump. going to leave it stardard till i got the cash to do it up.
yeh once its on ill be happy to post up how it goes, after all its so hard to find info so im happy to share.

Great to hear how it goes. If the engine is a factory TD42T GU engine, the pumps apparantly max out at ~ 90cc and you should get ~ 520-540nm @ crank, ~ 120-130rwkw providing you have an excellent intercooler and exhaust and ~ 18psi. That is the case with the late partly electronic pump (timing electronic, fueling is still mech though)

A stated above a STD pump will make 130RwKw on 35's when tuned correctly but remember that an efficient intercooler will mask some of the inherent problems with really tight turbine housings and high EGT's and turbine back pressure that go along with it . I am currently hearing of a LOT off failures of the 2860RS because they are used in rediculous situations where this exact thing is happening.

Sometimes better to lose 200 RPM spool time than put a turbo in an environment that it shouldn't be in.

[KiwiBacon]

A stated above a STD pump will make 130RwKw on 35's when tuned correctly but remember that an efficient intercooler will mask some of the inherent problems with really tight turbine housings and high EGT's and turbine back pressure that go along with it . I am currently hearing of a LOT off failures of the 2860RS because they are used in rediculous situations where this exact thing is happening.

Sometimes better to lose 200 RPM spool time than put a turbo in an environment that it shouldn't be in.

What sort of drive pressures are you seeing?

[UGOTNUFN]

A stated above a STD pump will make 130RwKw on 35's when tuned correctly but remember that an efficient intercooler will mask some of the inherent problems with really tight turbine housings and high EGT's and turbine back pressure that go along with it . I am currently hearing of a LOT off failures of the 2860RS because they are used in rediculous situations where this exact thing is happening.

Sometimes better to lose 200 RPM spool time than put a turbo in an environment that it shouldn't be in.

What sort of drive pressures are you seeing?

Up to 3 times nominal boost pressures on some of these very tight turbine housinged setups which is resulting in excessive heat soak into bearing areas hence cokeing oil and bearing damage. A roller bearing wont put up with this for a minute as they have no real volume of flushing oil for lubrication or cooling.

I hear stories of people saying they keep blowing turbo to manifold gaskets,no shit. turbine back pressures are not being taken into account enough. "oh but it spools really quick" great but it aint real reliable!!!!

[GU-ish]

interesting info. i went to the 2871. couldnt find much info on people using them but i thought id give it a dip as people said the 2860 dropped off up the the rev range

[KiwiBacon]

Up to 3 times nominal boost pressures on some of these very tight turbine housinged setups which is resulting in excessive heat soak into bearing areas hence cokeing oil and bearing damage. A roller bearing wont put up with this for a minute as they have no real volume of flushing oil for lubrication or cooling.

I hear stories of people saying they keep blowing turbo to manifold gaskets,no shit. turbine back pressures are not being taken into account enough. "oh but it spools really quick" great but it aint real reliable!!!!

That's surprisingly high. I once hit 4x boost, but I had to fit an extremely small turbine to get that (T2 with 0.49 housing). I was only getting double boost maximum (40psi for 20psi) with a T25 on a 3.9 litre Isuzu. The Isuzu is lower revving (3,600) but the differences aren't that big. It could deliver more boost than drive pressure below 2000rpm if the EGT's were above 650C.
Have you measured drive pressure on the stock Hitachi turbo?

[UGOTNUFN]

Up to 3 times nominal boost pressures on some of these very tight turbine housinged setups which is resulting in excessive heat soak into bearing areas hence cokeing oil and bearing damage. A roller bearing wont put up with this for a minute as they have no real volume of flushing oil for lubrication or cooling.

I hear stories of people saying they keep blowing turbo to manifold gaskets,no shit. turbine back pressures are not being taken into account enough. "oh but it spools really quick" great but it aint real reliable!!!!

That's surprisingly high. I once hit 4x boost, but I had to fit an extremely small turbine to get that (T2 with 0.49 housing). I was only getting double boost maximum (40psi for 20psi) with a T25 on a 3.9 litre Isuzu. The Isuzu is lower revving (3,600) but the differences aren't that big. It could deliver more boost than drive pressure below 2000rpm if the EGT's were above 650C.
Have you measured drive pressure on the stock Hitachi turbo?

Drive pressures on unmodified factory HT18 setups will go as high as 5 times nominal boost which is why i WILL NOT tune a TD42 that has a STD HT18, recipe for disaster over time. Remember that is at 8Psi and some people insist on turning them up to 12-13Psi unmodified.

[chunks]

So would a a 2876 work ok on a GU (06) with a standard pump, 3" exhaust and upgraded intercooler for say 130rwkw? Or would it be better to go the 2871?

[UGOTNUFN]

So would a a 2876 work ok on a GU (06) with a standard pump, 3" exhaust and upgraded intercooler for say 130rwkw? Or would it be better to go the 2871?

If you want a laggy POS with no driveability down low it will work fine!!!!

What do you want from your vehicle,driveability or dyno queen.

[RIZZO]

hey mate just go inbetween i did gt2871r .64 rear and 56trim should be right i find the 2860r to small for a 42td run out of puff to early cheers

yep agree

[chunks]

So would a a 2876 work ok on a GU (06) with a standard pump, 3" exhaust and upgraded intercooler for say 130rwkw? Or would it be better to go the 2871?

If you want a laggy POS with no driveability down low it will work fine!!!!

What do you want from your vehicle,driveability or dyno queen.

Nah I want driveability of course, vehicle is used everyday and for touring.

[KiwiBacon]

Good drivability and a 130 rwkw goal are quite different.

[chunks]

Why is that? I just want the power so i can hold gears better on hills, overtake with more ease etc. The truck rarely gets revved past 3 grand, 3500rpm is flogging it for me.

[KiwiBacon]

Why is that? I just want the power so i can hold gears better on hills, overtake with more ease etc. The truck rarely gets revved past 3 grand, 3500rpm is flogging it for me.

In that case, 130 rwkw isn't what you want. You actually want a big fat torque curve which delivers max boost just below your open road cruising rpm. So when you hit a hill the engine gains boost and torque if the revs drop a bit, rather than losing boost and torque as your average dyno queen will.
So if you cruise at 2200rpm, you want max boost to be there by 2000rpm at the latest.
A big turbo dyno queen might not hit max boost until 2500-3000rpm, which means you need to go down gears and rev it to get anywhere.

It's very easy to hit a big power number, you simply pick the biggest turbo that will give the boost you need at the max power rpm. But drivability goes right out the window.

[UGOTNUFN]

Why is that? I just want the power so i can hold gears better on hills, overtake with more ease etc. The truck rarely gets revved past 3 grand, 3500rpm is flogging it for me.

So all you need is a turbo that is suited to your application.

If you really want a BB turbo then get a 2860 and run it at 10 pound with no intercooler or 12-14 intercooled.

If youre open to suggestions get and fit a DTS turbo kit and it will do what you want all day everyday for the next 200K

[chunks]

Thanks fellas, might have a chat to JPC when I'm ready to upgrade.